Not exactly scam, but depends on who and how they sell it. The permeate pump is certified, made of harmless material, and won't fall apart, but it is the magic bullet as claimed in the manufacturer's Aquatec website? No. But since they only sell it to distributors, they give you no specification and they are not responsible how you use it. But now these companies know that nothing can stop people selling things to individuals on eBay, they are a bit careful on their website, in order not to develop a scandal.
Many pumps are sold to retrofit existing systems. But notice the 75 psi feed input on the main diagram on their website. If you haven't got that pressure, it very doubtful it will work well. And if you got all that pressure, it's doubtful if you need a pump to get good results.
Standard main water pressure depends on water district, but should be 50 psi, which is the value for sprinkler specification. You may get higher pressure if you live uphills in individual houses, where the water pressure gradually decrease downhills to 50 psi for houses at the bottom. In this case you need a pressure regulator, which is usually factory preset to 50 to 60 psi, with 75 psi as the absolute rating. So basically, now that the permeate pump isn't new anymore, Aquatec is basically saying you need a booster pump without admitting it. A booster pump cost twice as much and gives you a lot of improvement if your feed is just 50 psi. It's crazy if you use a booster pump plus a permeate pump. Since I have 75 psi without the need for a booster pump, I'm OK. It wouldn't work well for 60 psi, and I can prove it.
When the tank is empty, that is, no back pressure to the membrane, the membrane sees the full pressure of about 70 psi. The pump is supposed to maintain the back pressure to at most a few psi so the full 70 psi pressure is maintained at all times. With the right flow restrictor, there should be enough pressure and flow in the brine/concentrate to do that. But I found out that the recovery rate have to be high at about 25%. Which means that the drinking water to waste water ratio is 1:3. This is far from the usual 1:4, or 20%, and far from the specified Filmtec membrane recovery of 15%.
But all is not lost. At 70 psi, even 25% recovery gives 98% stable rejection, which is the same specified rejection at 50 psi and 15% recovery. So with a virtual booster pump, and a permeate pump, I can't get better rejection but I waste half the water, 1:3 recovery instead of 1:6 recovery.
It won't work if you don't have 75 psi main feed. Say at 60 psi feed, you have about 50 psi across the membrane, and clearly at this pressure, you need 15% recovery to achieve anywhere near 98% rejection. 25% recovery is far off.
It's doubtful if you need any pump when you have 75 psi pressure. A 75 gpd membrane becomes 110 gpd which is a hell lot of water. But since the pressure is constant across the membrane, it's easy to design your system, and the performance is guaranteed under all circumstances. In other words, peace of mind.
In pumpless systems, basically the water is excellent when the tank is empty. Then the water tend to get worse as the tank fills up, or you waste a lot more water without realizing it, that's what Aquatec is trying to market their pumps. With typical usage, the system works most often when only a few cup or a kettle of water is being drawn from the tank. The water is worse or wasting most water when the pressure across the membrane is often 50% to 33% of an empty tank.
Actually I would like to write software to design residential systems. Dow has free software but far too complex and did not give out parameters for the residential membranes. So I couldn't do anything but to use 75 psi main pressure. The pressure is constant and everything is constant so it's easy to design.
And now the cutoff valve. It's not cheap at 1/3 of the pump price. But does it worth it? Nobody claims that it's necessary but say enough that you will buy it. I was surprised to find out that the valve don't cutoff at 90%, but about the same as the old valves about 66%. I talked to the distributors and manufacturer and it seems that they are well prepared. The distributor send me over to the manufacturer, who promise to test it and replace it if it's defective. But I am not to expect 90%, but 85% depending on pressure.
I almost sent it off when I realized that now the cutoff pressure of my tank will be the main pressure of most people, at 50 psi. It will be crazy to increase that to 65 psi. I don't need that and the pump may not work at that pressure. Also, the valve turn back on at 30 psi, giving 20 psi of hysteresis so the system won't turn on and off whenever people drawn a glass of water or a kettle of water. I don't know if my old valve do that. But since the new valve has JG connectors that are easy for me to measure things, and that the tubings are fitted already, I rather not go back to the old one.
Previously I have doubts about measuring pressure when water is flowing. But I find that it's very accurate, the dynamic pressure into the tank equals exactly the static pressure when the tank is isolated. After all, what else can it be? Now I left the pressure gauge dangling in a T piece somewhere in the water path. And since I needed a tank shutoff valve as an adapter for the standard gauge, I can shut off the valve so the gauge isn't in contact with potable water when not in use.
Showing posts with label reverse osmosis. Show all posts
Showing posts with label reverse osmosis. Show all posts
Saturday, September 22, 2007
Wednesday, September 12, 2007
The perfect reverse osmosis system
Perfect also means a good price :-)
The feed shut off valve is not enough. It takes forever to shut off the system and restart. I suggest to add a plastic ball valve right after the feed valve. Surprisingly, the ball valve carried at Lowes carry a cancer causing material warning, but it's sold along side NSF approved tubings. I would buy a valve with John Guest connectors. And since JG seemed to be patented, there's always a minute but ultra fine JG symbol somewhere, even though the manufacturer's name wasn't on the component. This is very typical. Manufacturers don't normally make all the component of an RO system. So they mainly sell to OEM's, unmarked or marked with the OEM's name. BTW, JG is also a company producing many components.
You can easily find NSF approved 1/4" tubing in hardware stores, for fridge ice makers. For the filter housings, what can go wrong? It's hard to check if those components are NSF approved, as most makers sell them to OEM's. And then the whole system is approved rather than individual components. But I bet all housings are made of FDA approved food grade plastics, and that any housing looks like any others. But I'm not so sure about the O-rings used to seal the filters. There are NSF or FDA approved O-rings on sale fit for standard housings. And there are approved silicon grease to be applied on the O-rings to seal.
There are typically up to 3 pre filters about 10" long for residential use. The main purpose is to remove chlorine which attacks the membrane. But I made the mistake of choosing too good prefilters. The worse mistake is to use a 0.2 micron ceramic filter. When I looked at the data sheet, the pressure drop across the filter is 15 psi, though at a very high flow rate which doesn't occur at residential systems. So at 50 psi input feed, you could lose a lot of pressure just across one filter alone. The filters to buy are Matrikx branded. They have a stable and clear line of products. They have a good name and a lot of systems use them (I guess). They provide datasheets. You can get the top ones at as low as $10.
The static pressure is easy to measure. A pressure gauge costs a few dollars from hardware stores. Screw it on a garden tap, 3/4", and you get the static pressure, when all other taps are closed. For 1/4" RO systems, you just unscrew the 3/4" adapter typical on gauges, and you can screw the gauge directly into a JG ball valve for RO tanks. Now you just insert any tube into the valve and you get the static pressure with the valve open. But measuring the pressure when water is flowing is tricky. If the water don't flow, there's no pressure drop across the pre filters. I've seen attaching a gauge to a T adapter. Water is flowing straight through and the pressure is seemed to measure perpendicularly to the flow.
Filtered drinking water is measured in gpd, gallon per day, while the stated flow rate for pre-filters is typcally gpm, per minute. So the stated pressure drop at the high flow rate may not apply at very low flow rates. Anyway since I cannot know this, I minimize the pressure drop by choosing suitable filters.
I'll start with a 5 micron sediment filter, if you water supply isn't that dirty. Coarser filter is associated with larger dirt capacity and less pressure drop, a few psi. Then the 20,000 gal carbon chlorine filter is a no brainer. If you don't really know how much water you drink, it guarantees you only need to change filter once a year. If you know, you save money and time because the chlorine capacity is a lot larger than other filters, you only need to change filters once a long time. I estimated that the water passing through my filter will be 5,000 to 10,000 gal, so I only need to change filters once 2 to 4 years, considering the chlorine capacity alone. It also good for filtering VOC if by chance you got it, volatile organic compounds, which are basically vapor gas that the RO membrane can't deal with. The pressure drop is less than 3.5 psi and the size is about 0.6 micron.
It just happened that I have a 3 stage housing so I have to pick one more. Another same carbon filter is OK but there are a lot of other choices probably for non RO systems. The mistake I made was picking a 0.2 um one with a psi drop of 15, making it unsuitable for RO systems. The choice is between certified lead or bacteria rejection. Since my water feed is very decent, and since the membrane will deal with that at sub micron levels, I settled on a 0.5 um carbon filter with 8 psi drop, with half the chlorine capacity. There is some cyst reduction, bacteria that isn't killed by chlorine. Other reasons are price and availability.
The most important component used to be the membrane. But as I said, pumps cost a lot more. The only membrane to get is Filmtec, certified for 96 to 98% rejection. And 75 gpd is the only capacity you want. Any larger the rejection drops to 90%, and any other brands is just as good. Even if you don't drink that much water, the tank refills fast. And since you don't have 50 psi as assumed by most components, you have more design flexibility and more choice of good filters. After all, it's just $30.
15% to 20% of water pass through the membrane, while the rest go down the drain. What makes water pass through the membrane is a flow restrictor on the brine side (waste water) of the membrane. Interestingly, almost certainly you have a wrong flow restrictor. If you have a 75 gpd membrane, waste water is 4 times that, arriving at about 800 mL per minute, which is the standard restrictor to use. But, the Filmtec membrane recovery is 15% rather than 20%, which requires a larger capacity. Also, instead of 75 gpd at 50 psi, you have 40 psi across the membrane if you are lucky. And for pumpless systems, you have just about 20 psi when the tank is almost full.
You don't have much control over pressure unless you have a booster pump to vary the input psi, and a permeate pump to maintain a constant pressure across the membrane. In my area we need a pressure regulator so I can increase that to 100 psi risking bursting pipes anytime, or decrease at the expense of weaker showers. Other than that you can buy filters with larger or smaller psi drops. However since you can't measure that reliably, I suggest to get a few flow restrictors, test the system performance with a TDS meter, pick the best one and return the rest !!
It's worthwhile to make a bypass path across the restrictor, controlled by a ball valve. It's called flushing the membrane when you by pass the restrictor, when all water goes to drain to clean the membrane. With JG connectors, it only cost you a minute to make. NSF components are not required at the brine side. Expensive systems used to have that path, and of course a timer to flush everyday for a few minutes. Membranes need flushing regularly only if your system is at 98% I guess. It's easy to achieve over 95% and never flush. At $30 it's worthwhile to change the filter every year. But if you use it for a few years for the full design life, you feel better to flush every few months or a year. The waste water are black, mostly carbon resides from the filters.
After the invention of the "affordable" permeate filter, it's clear that prior pumpless systems are toys. No matter how good your filters and membranes are, you only operates at a fraction of the pressure. The pump comes with a new hydraulic valve, which cutoff the supply when the tank pressure is 90% of the feed, and turns on the supply when the pressure drops below 70%. Since the membrane always see full pressure, the high cut off allows the tank to fill more water at higher pressure, and the on pressure prevents starting the system every time for a minute when you just pour a glass of water. The higher pressure is important if previously your RO water can't get through to the fridge to make ice. Previously standard valves cut off at 66%, leaving you with 33% pressure across the membrane. Permeate pump not only save you water, because less water flows through, you get longer filter and membrane life.
The final filter is always after the tank. I wondered why. Until one day I tasted the tank water and it smells and taste like rubber. I think it's a taste of the bladder inside for cheap tanks at least. It's also a good idea to filter the water when you drink it, not when you store it in a tank. I always use NSF certified Omnipure. Unlike Matrikx carbon block filters, which are designed for chlorine capacity and minimize carbon residues clogging the membrane, the final filters are carbon granulates design for maximum bad taste reduction. And I can vouch for it. These filters are smaller and have a much lower capacity as the drinking water to total water ratio is at least 1 to 4 or 6. But still you may need to change every 6 month instead of a year.
Cheap tanks rust easily on the outside and taste like rubber. They also lost pressure fast. There's a tire like bladder inside. When you lost pressure, you need to pump water out using a tire pump, measure the air pressure at 7 psi for typical tanks. Of course you better get a new tank when you lost pressure. The one to get is Flowmatic RO Pro tank. It's NSF listed. It's plastic so it doesn't rust, at least on the outside. The shape and color is a lot more pleasant than metal tanks. It fits well under the sink like a tall slim guy rather than a short fat guy with a beer belly. 4 gallon total is about the largest size that fit comfortably under the sink with space for other things. Practically you get only 2+ gallon for pumpless systems, or 3+ with a permeate pump. You also get a nice reserve in earthquake zones, enough for at least 6 people's maximum drinking needs for one day, but a least a few days for survival.
You have little choice about the faucet. A designer faucet cost you more than all the other components. Most people use Touch Flo faucets, look decent, cheap, and NSF listed. There was a settlement about lead many years ago. So they won't make the mistake twice. An ordinary drill and a special bit from hardware stores will make an extra hole on your sink, but depending on the material, I still have nightmares about it. But in my neighborhood, you can't find people to come in and drill a hole for you, not at a price you want to pay. You rather hire any heavy machinery you need from the hardware stores and blast everything yourself.
You need an air gap somewhere to prevent back flow of waste water. If the law allows you can use a check valve instead. Air gap at the faucet is a bad idea unless the faucet comes with tubings attached. It's a nightmare to attach all the tubes under the sink for a compact faucet at the very corner. You can use the air gap for the dishwasher. There are air gaps designed for that with extra RO input.
A digital TDS meter is a must. It's cheap and compact anyway. It's a measure of the conductivity of the water, which reflects directly the dissolved solids in the water. And since only the membrane can remove dissolved solids, the meter tells you how well your system is doing, if put together correctly at all. Typically for hard water, the supply is 400 ppm. If the RO water is 20 ppm, you get 95% rejection. It can be addictive. If you are a Monk person, it's worthwhile to get one of those that mounted on the sink to give readings continuously.
The other parameters that indicates your system is working correctly is a flow rate meter. But it's rather not necessary. You just need a measuring cup and a stopwatch. You get a good idea of the flow rate out of the restrictor and out of the membrane (when the tank is shut off). Restrictors can be inaccurate because of deposits, which is at higher concentration at the brine side.
Now there are low cost total volume flow meters on the market made of FDA approved plastic. You can program 5 reminders to change your filters according to total volume passing through. Nobody have a good idea how much water they actually use. Filters are either changed prematurely along with all other filters, or way too late. So the saving in filter cost will make the meter virtually free. You also get peace of mind. But you need to know the design capacity of the filters. But actually you need two, since there are three flow volumes in the system, the supply, the permeate (drinking) and brine (waste). Since the permeate and brine are never exactly 1:4 or any other ratio as designed, you need two meters to get all the three flow volumes, unless you have a good idea what the measured ratio actually is.
You need to disinfect and clean the system on a regularly basis, say once a year. The membrane is tricky if you decide to keep it for a few years. It can only tolerate low concentrations of chemicals and you need to pump the solutions through the membrane constantly for limited time. The details are on their website. I would rather flow it away after a year, or just soak it. To disinfect you need H2O2 from pharmacy and dilute about 10 times (check website). I'll soak it in the filter housing instead of pumping it for the recommended period. I have no pump. Then I'll put fresh solution in the empty filter housings, put the membrane back in it's housing, and turn on the feed supply. The H2O2 gets pumped across the membrane, but further diluted.
But if you actually bother to disinfect the membrane, you might just as well buy NaOH and HCL solutions from science stores and perform the alkaline and acidic cleaning steps as recommended.
Before the membrane, you can just as well pump higher concentration of cleaning and disinfecting solutions around the system, the tank, the tubes and the filter housings. Then using the tank to pump the solutions all the way to the fridge. Of course you need to pump a lot of fresh water to get rid of the solutions, and throw away the ice.
I think that's about it. Now the cost.
JG Valve's and T's $30
Filter housing $60
Filter 1 $10
Filter 2 $10
Filter 3 $15
Filter 4 $15
Membrane $40
Pump $45
cut-off valve $15
Tank $70
Faucet $30
TDS meter $20
Flow meter $30
Total $390
This is the retail component prices. If you buy in bulk and sell whole systems, you make a decent profit without much work. The JG connectors are a snap to use.
The feed shut off valve is not enough. It takes forever to shut off the system and restart. I suggest to add a plastic ball valve right after the feed valve. Surprisingly, the ball valve carried at Lowes carry a cancer causing material warning, but it's sold along side NSF approved tubings. I would buy a valve with John Guest connectors. And since JG seemed to be patented, there's always a minute but ultra fine JG symbol somewhere, even though the manufacturer's name wasn't on the component. This is very typical. Manufacturers don't normally make all the component of an RO system. So they mainly sell to OEM's, unmarked or marked with the OEM's name. BTW, JG is also a company producing many components.
You can easily find NSF approved 1/4" tubing in hardware stores, for fridge ice makers. For the filter housings, what can go wrong? It's hard to check if those components are NSF approved, as most makers sell them to OEM's. And then the whole system is approved rather than individual components. But I bet all housings are made of FDA approved food grade plastics, and that any housing looks like any others. But I'm not so sure about the O-rings used to seal the filters. There are NSF or FDA approved O-rings on sale fit for standard housings. And there are approved silicon grease to be applied on the O-rings to seal.
There are typically up to 3 pre filters about 10" long for residential use. The main purpose is to remove chlorine which attacks the membrane. But I made the mistake of choosing too good prefilters. The worse mistake is to use a 0.2 micron ceramic filter. When I looked at the data sheet, the pressure drop across the filter is 15 psi, though at a very high flow rate which doesn't occur at residential systems. So at 50 psi input feed, you could lose a lot of pressure just across one filter alone. The filters to buy are Matrikx branded. They have a stable and clear line of products. They have a good name and a lot of systems use them (I guess). They provide datasheets. You can get the top ones at as low as $10.
The static pressure is easy to measure. A pressure gauge costs a few dollars from hardware stores. Screw it on a garden tap, 3/4", and you get the static pressure, when all other taps are closed. For 1/4" RO systems, you just unscrew the 3/4" adapter typical on gauges, and you can screw the gauge directly into a JG ball valve for RO tanks. Now you just insert any tube into the valve and you get the static pressure with the valve open. But measuring the pressure when water is flowing is tricky. If the water don't flow, there's no pressure drop across the pre filters. I've seen attaching a gauge to a T adapter. Water is flowing straight through and the pressure is seemed to measure perpendicularly to the flow.
Filtered drinking water is measured in gpd, gallon per day, while the stated flow rate for pre-filters is typcally gpm, per minute. So the stated pressure drop at the high flow rate may not apply at very low flow rates. Anyway since I cannot know this, I minimize the pressure drop by choosing suitable filters.
I'll start with a 5 micron sediment filter, if you water supply isn't that dirty. Coarser filter is associated with larger dirt capacity and less pressure drop, a few psi. Then the 20,000 gal carbon chlorine filter is a no brainer. If you don't really know how much water you drink, it guarantees you only need to change filter once a year. If you know, you save money and time because the chlorine capacity is a lot larger than other filters, you only need to change filters once a long time. I estimated that the water passing through my filter will be 5,000 to 10,000 gal, so I only need to change filters once 2 to 4 years, considering the chlorine capacity alone. It also good for filtering VOC if by chance you got it, volatile organic compounds, which are basically vapor gas that the RO membrane can't deal with. The pressure drop is less than 3.5 psi and the size is about 0.6 micron.
It just happened that I have a 3 stage housing so I have to pick one more. Another same carbon filter is OK but there are a lot of other choices probably for non RO systems. The mistake I made was picking a 0.2 um one with a psi drop of 15, making it unsuitable for RO systems. The choice is between certified lead or bacteria rejection. Since my water feed is very decent, and since the membrane will deal with that at sub micron levels, I settled on a 0.5 um carbon filter with 8 psi drop, with half the chlorine capacity. There is some cyst reduction, bacteria that isn't killed by chlorine. Other reasons are price and availability.
The most important component used to be the membrane. But as I said, pumps cost a lot more. The only membrane to get is Filmtec, certified for 96 to 98% rejection. And 75 gpd is the only capacity you want. Any larger the rejection drops to 90%, and any other brands is just as good. Even if you don't drink that much water, the tank refills fast. And since you don't have 50 psi as assumed by most components, you have more design flexibility and more choice of good filters. After all, it's just $30.
15% to 20% of water pass through the membrane, while the rest go down the drain. What makes water pass through the membrane is a flow restrictor on the brine side (waste water) of the membrane. Interestingly, almost certainly you have a wrong flow restrictor. If you have a 75 gpd membrane, waste water is 4 times that, arriving at about 800 mL per minute, which is the standard restrictor to use. But, the Filmtec membrane recovery is 15% rather than 20%, which requires a larger capacity. Also, instead of 75 gpd at 50 psi, you have 40 psi across the membrane if you are lucky. And for pumpless systems, you have just about 20 psi when the tank is almost full.
You don't have much control over pressure unless you have a booster pump to vary the input psi, and a permeate pump to maintain a constant pressure across the membrane. In my area we need a pressure regulator so I can increase that to 100 psi risking bursting pipes anytime, or decrease at the expense of weaker showers. Other than that you can buy filters with larger or smaller psi drops. However since you can't measure that reliably, I suggest to get a few flow restrictors, test the system performance with a TDS meter, pick the best one and return the rest !!
It's worthwhile to make a bypass path across the restrictor, controlled by a ball valve. It's called flushing the membrane when you by pass the restrictor, when all water goes to drain to clean the membrane. With JG connectors, it only cost you a minute to make. NSF components are not required at the brine side. Expensive systems used to have that path, and of course a timer to flush everyday for a few minutes. Membranes need flushing regularly only if your system is at 98% I guess. It's easy to achieve over 95% and never flush. At $30 it's worthwhile to change the filter every year. But if you use it for a few years for the full design life, you feel better to flush every few months or a year. The waste water are black, mostly carbon resides from the filters.
After the invention of the "affordable" permeate filter, it's clear that prior pumpless systems are toys. No matter how good your filters and membranes are, you only operates at a fraction of the pressure. The pump comes with a new hydraulic valve, which cutoff the supply when the tank pressure is 90% of the feed, and turns on the supply when the pressure drops below 70%. Since the membrane always see full pressure, the high cut off allows the tank to fill more water at higher pressure, and the on pressure prevents starting the system every time for a minute when you just pour a glass of water. The higher pressure is important if previously your RO water can't get through to the fridge to make ice. Previously standard valves cut off at 66%, leaving you with 33% pressure across the membrane. Permeate pump not only save you water, because less water flows through, you get longer filter and membrane life.
The final filter is always after the tank. I wondered why. Until one day I tasted the tank water and it smells and taste like rubber. I think it's a taste of the bladder inside for cheap tanks at least. It's also a good idea to filter the water when you drink it, not when you store it in a tank. I always use NSF certified Omnipure. Unlike Matrikx carbon block filters, which are designed for chlorine capacity and minimize carbon residues clogging the membrane, the final filters are carbon granulates design for maximum bad taste reduction. And I can vouch for it. These filters are smaller and have a much lower capacity as the drinking water to total water ratio is at least 1 to 4 or 6. But still you may need to change every 6 month instead of a year.
Cheap tanks rust easily on the outside and taste like rubber. They also lost pressure fast. There's a tire like bladder inside. When you lost pressure, you need to pump water out using a tire pump, measure the air pressure at 7 psi for typical tanks. Of course you better get a new tank when you lost pressure. The one to get is Flowmatic RO Pro tank. It's NSF listed. It's plastic so it doesn't rust, at least on the outside. The shape and color is a lot more pleasant than metal tanks. It fits well under the sink like a tall slim guy rather than a short fat guy with a beer belly. 4 gallon total is about the largest size that fit comfortably under the sink with space for other things. Practically you get only 2+ gallon for pumpless systems, or 3+ with a permeate pump. You also get a nice reserve in earthquake zones, enough for at least 6 people's maximum drinking needs for one day, but a least a few days for survival.
You have little choice about the faucet. A designer faucet cost you more than all the other components. Most people use Touch Flo faucets, look decent, cheap, and NSF listed. There was a settlement about lead many years ago. So they won't make the mistake twice. An ordinary drill and a special bit from hardware stores will make an extra hole on your sink, but depending on the material, I still have nightmares about it. But in my neighborhood, you can't find people to come in and drill a hole for you, not at a price you want to pay. You rather hire any heavy machinery you need from the hardware stores and blast everything yourself.
You need an air gap somewhere to prevent back flow of waste water. If the law allows you can use a check valve instead. Air gap at the faucet is a bad idea unless the faucet comes with tubings attached. It's a nightmare to attach all the tubes under the sink for a compact faucet at the very corner. You can use the air gap for the dishwasher. There are air gaps designed for that with extra RO input.
A digital TDS meter is a must. It's cheap and compact anyway. It's a measure of the conductivity of the water, which reflects directly the dissolved solids in the water. And since only the membrane can remove dissolved solids, the meter tells you how well your system is doing, if put together correctly at all. Typically for hard water, the supply is 400 ppm. If the RO water is 20 ppm, you get 95% rejection. It can be addictive. If you are a Monk person, it's worthwhile to get one of those that mounted on the sink to give readings continuously.
The other parameters that indicates your system is working correctly is a flow rate meter. But it's rather not necessary. You just need a measuring cup and a stopwatch. You get a good idea of the flow rate out of the restrictor and out of the membrane (when the tank is shut off). Restrictors can be inaccurate because of deposits, which is at higher concentration at the brine side.
Now there are low cost total volume flow meters on the market made of FDA approved plastic. You can program 5 reminders to change your filters according to total volume passing through. Nobody have a good idea how much water they actually use. Filters are either changed prematurely along with all other filters, or way too late. So the saving in filter cost will make the meter virtually free. You also get peace of mind. But you need to know the design capacity of the filters. But actually you need two, since there are three flow volumes in the system, the supply, the permeate (drinking) and brine (waste). Since the permeate and brine are never exactly 1:4 or any other ratio as designed, you need two meters to get all the three flow volumes, unless you have a good idea what the measured ratio actually is.
You need to disinfect and clean the system on a regularly basis, say once a year. The membrane is tricky if you decide to keep it for a few years. It can only tolerate low concentrations of chemicals and you need to pump the solutions through the membrane constantly for limited time. The details are on their website. I would rather flow it away after a year, or just soak it. To disinfect you need H2O2 from pharmacy and dilute about 10 times (check website). I'll soak it in the filter housing instead of pumping it for the recommended period. I have no pump. Then I'll put fresh solution in the empty filter housings, put the membrane back in it's housing, and turn on the feed supply. The H2O2 gets pumped across the membrane, but further diluted.
But if you actually bother to disinfect the membrane, you might just as well buy NaOH and HCL solutions from science stores and perform the alkaline and acidic cleaning steps as recommended.
Before the membrane, you can just as well pump higher concentration of cleaning and disinfecting solutions around the system, the tank, the tubes and the filter housings. Then using the tank to pump the solutions all the way to the fridge. Of course you need to pump a lot of fresh water to get rid of the solutions, and throw away the ice.
I think that's about it. Now the cost.
JG Valve's and T's $30
Filter housing $60
Filter 1 $10
Filter 2 $10
Filter 3 $15
Filter 4 $15
Membrane $40
Pump $45
cut-off valve $15
Tank $70
Faucet $30
TDS meter $20
Flow meter $30
Total $390
This is the retail component prices. If you buy in bulk and sell whole systems, you make a decent profit without much work. The JG connectors are a snap to use.
Tuesday, September 11, 2007
The perfect water
First of all, most reverse osmosis system are designed to have a recovery of 20%, that is, for every 1 cup you drink, you throw away 4 cup. That sounds a lot, but you actually don't drink that much water. Baths and lawns are a lot more wasteful. More so is flushing the toilet. Somewhere in the world use sea water or reclaimed water to flush. Also, bottle water, such as the famous Fuji water now widely available in Trader Joe, seems a lot more wasteful, pumping up deep ancient water and bring it over from so far away, in plastic bottles. Also many beverages you drink use RO water anyway. In good restaurants, if you don't want bottled water, they will give you tap water, filtered to taste good. It's worthwhile to include RO to avoid liabilities as bacteria and virus can hardly pass through. It's easy to achieve zero waste. You can feed the water to your irrigation system, or pump it back to the hot water supply.RO systems used to be very expensive, $1000?, and still are, $500?. Some years back some cheap RO systems appear on the market aimed at the masses at $100. The performance in terms of rejection rate of total dissolved solids (TDS) is 85%, compared to top of the line systems at 98%. 85 is a lot less than 98, but filtering out 85% of what need not be there sounds enough for a try. The DS are basically the hardness of the water, naturally occurring materials. But here we use Colorado river which is really hard. And if something goes wrong for a short while in the public system, softening the impact by 85% isn't that bad. And if you can filter out 85% of the bacteria, that's good enough without costing an arm and a leg. It's not that I couldn't afford expensive systems. But like computers, I don't know what components they put in. You cannot test it, for example, how much lead it rejects. You have to trust them. But I rather not.
But the cheap pumpless systems are a joke. The stated performance is for full water pressure, typically 50 psi (sorry rest of the world). But once the system starts working, the pressure across the RO membrane falls. These systems typically stops when the tank pressure reaches 30 psi, by this time the pressure across the membrane is only 20 psi, a fraction of the stated performance.
Typically small manufacturers don't know what exactly happens as the operating points drift away from the optimum point where all the components are guaranteed. But as long as the final TDS reading looks good, they are selling it. Typically, the rejection rate maintains at low pressure, at the expense of wasting much more water! Not just 20%, but 10% and less.
To control the pressure, you need a pump. But pump's able to deal with 50 psi are not toys. Just a booster pump cost more than a cheap RO system. The alternative is to use an open tank and let the RO water flows into the tank slowly. So you are fortunate if you are a fish. For aquarium applications, the water is as good as any top of the line systems. But without a pressurized tank, you either go fetch water from under sink, or use a delivery pump. So a pump again, though at lower pressure the pump is cheaper, but not by a lot needing NSF testing. And you start to worry about the air quality, and air borne bacteria. Until the permeate pump, which is a lot cheaper without electricity and at lower pressure. Basically it's a weak hydraulic pump, pumping filtered water into the pressurized tank. With a pump, the pressure of the tank is isolated from the membrane. So the membrane is seeing the full water pressure all the time.
I'm going to describe safe materials and the correct design of an RO system. Indeed if there are not so many one man company selling put together systems, I may start selling too.
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